the harry potter universe, j.k. rowling's creation, has spell bound millions. now, rowling has left her wizarding world behind for an adult novel called "the casual vacancy." you've gone from the ultimate fantasy to the ultimate reality. >> i've gone from dragons and unicorns and all the fun that's involved in writing that, to a book that intensely personal. that expresses a lot of my reality. >> reporter: rowling insists the book is not a memoir. but she did draw on the darker times of her life to craft her characters. >> we have an adult character in the book who has obsessive compulsive disorder. these are things i know from the inside. yeah. >> reporter: the ocd part of it, as well? >> when i was in my teens i had issues with ocd. >> reporter: how did it manifest? >> compulsions. checking things. very common. double-checking. triple-checking. >> reporter: some might wonder why rowling, an almost billionaire, would bother writing another book, putting her reputation on the line. how will you decide this book is a success? >> it won't sell as many as harry po